[Texstucker]

Hello,

I am a PM for a general contractor. Current project includes a set of high-rise grease ducts all in the same shaft (28 stories). Our mechanical subcontractor needs to weld the ductwork but the engineer hasn't provided enough space to get a welding mechanic in the shaft to weld the duct. The ductwork is 16 ga. black steel. I am arguing the welder needs to get fully in front of his work to see his work and get a quality weld.

Consider a 24x24 duct running adjacent to a concrete wall on one side. How far away from the wall does the duct need to be in order for a welder to get his body and the stick/wand behind the weld to do the work?

Thanks.

[tweake]

i wonder if you need to find someone that can mirror weld.
not to sure what you mean by grease duct, but the obvious thing is to have flanges on the duct lengths and bolt them together at certain points. ie weld several short lengths together with it hanging out in the centre of the space, where you can turn it etc. then put it against the wall and bolt the long lengths together.

[Poland308]

If it’s within arms length from where you can get your head. Then you might need to tape up some 12” mirror tiles, sold at most Home Depot stores. Then you need to be able to get your head and arms in position at the same time. If you can get good visibility then you can tig it with a mini rig. Needs about 4-6 inches for your hands.

[Poland308]

Or you hang down on the inside and weld it from in there.

[Texstucker]

Thanks, appreciate the responses.

[Coldman]

I find it interesting that you can get away with 16# for such a tall grease duct.
I'm used to seeing them about 1/4" when I was doing high rise down under. Reason being eventually the grease is going to catch fire and maybe go "poof". Extra thickness required to cope with the "poof" and minimise warping due to flame heat.

[Coldman]

We used to weld rated lifting lugs inside the top section, the roof crane would drop his hook down the shaft and and chain onto the lugs, lift the section up enough to slide another underneath in the kitchen and do a full penetration weld or bolt up flanges. Lift some more, weld or bolt another section in underneath etc and up she goes. Get to the top, install brackets, fit kitchen hood underneath, happy days.
If the crane is gone or can't get access to it, get a hydraulic winch set up top. Don't know where to get a hydraulic winch? Contact the nearest dry dock or ship repair contractor, they will point you in the right direction.

[Coldman]

Still can't get to the back? Cut a rectangular window in the front big enough for the welder to get in and weld the back joint from the inside, then weld the cut-out back in.